Some resources, such as web sites, permit users to post or otherwise provide content for an associated portion of the resource, such as a web page. These users may generate a large amount of unstructured content that implicitly or explicitly indicate each user's interests. The resource may further allow third-party content providers to provide third-party content items resources. Third party content providers may include advertisers or other providers of goods and/or services. For example, a first-party content provider of a resource devoted to golf may allow an online retailer that sells golf clubs to place third-party content items on the resource. In return, the third-party content provider may compensate the first-party content provider based on one or more measurements of traffic to the resource. In one example, the third-party content provider may pay the first-party content provider based on the number of impressions, i.e., the number of times the third-party content items were displayed on the resource to users. In another example, the third-party content provider may pay the first-party content provider based on the number of users that clicked on the third-party content items and were redirected to the third-party content provider's resource and/or made a purchase from the third-party content provider's resource.